Currently the most common method of manufacturing flexible containers uses heat sealing or welding together of films or sheets as the joining method. Heat sealing of plastic film has three components: 1) Heat: sufficient to melt plastic layers to fuse; 2) Pressure: Sufficient to ensure a good seal; and 3) Dwell Time: sufficient time for the heat and pressure to be applied to material to achieve seal. Beyond dwell time, it takes more time for the heat sealed area to cool enough to become solid. Heat seals are usually produced by “radiant”, “impulse” or “inductive” methods. Methods of producing heat seals range from manual to fully automatic either in an “intermittent” (start/stop) or continuous motion (rotary or moving platen) Production rates of heat sealing are in the range of 100 to 135 feet of film per minute. This production rate has not obtained significant increases in speed for many years.
There are a number of processes that create roll stock at a factory using factory bonds to partially construct a flexible container while leaving one or more bonds (user bonds) to be completed by the user after the flexible container has been filled. One of the advantages of this two step (factory/user) sealing process is that shipment of roll stock rather than completed products is more efficient in that a relatively small volume of roll stock can contain the film necessary to create a very large volume of finished product. Given the distribution of companies with heat seal equipment that is used to make the final user bonds, it is desirable that new processes be compatible with heat sealing so that user bonds may be added using conventional heat sealing equipment.
One type of bond that is particularly useful is a hermetic seal bond. Such a bond is sufficient to prevent the migration of solids, liquids, and gases across the bond under normal operating conditions. Thus, a bond between two adjacent layers of film would be a hermetic seal bond if gas cannot pass through the bond to move from one side of the bond to the other side of the bond. To the extent that the product receives a user bond after filling at the user's location, the factory bonds may not fully encircle an area to form a closed volume so that volume is not yet hermetically sealed although portions of the perimeter of the volume have hermetic seal bonds.